Blood treatment apparatus with flow divider for limiting an electrical current

ABSTRACT

A blood treatment apparatus comprising: a blood treatment unit; a blood line configured to extract blood from a blood source, pass the blood through the blood treatment unit and deliver treated blood to a target vessel; and a fluid line configured pass treatment fluid through the blood treatment unit and deliver used treatment fluid to a fluid sink. A flow divider is arranged in the fluid line separates treatment fluid into to a first fluid section and a second fluid section, thereby electrically isolating the fluid sections such that electrical current flowing in the fluid line between the fluid sections is limited. Related manufacturing and verification methods are also described.

TECHNICAL FIELD

The invention relates to an apparatus with a blood treatment unitthrough which electrically conductive treatment fluid is passed fortreating blood.

BACKGROUND ART

Today blood treatment apparatuses are used for extracorporeal bloodtreatment and involves drawing blood from a patient, treating the bloodand returning the treated blood to the patient. For this purpose anextracorporeal blood flow circuit is used which is connected to a bloodvessel access of the patient, typically via one or more access devicessuch as needles or cannulas inserted into the blood vessel access.Depending on method of blood treatment, the blood may be withdrawn andreturned via the same blood vessel access or via separate blood vesselaccesses. Extracorporeal blood treatment includes hemodialysis,hemodiafiltration, hemofiltration, plasmapheresis etc.

The blood treatment apparatus is in principle an electrically poweredmachine that is fed with an electrical current. If an electrical failureoccurs in the blood treatment apparatus, there might be a risk that thepatient is subjected to an electrical shock which may have severeconsequences. Thus, it is vital that the blood treatment apparatus isdesigned such that it offers a high degree of electrical insulation forreducing the risk that an electrical current flows from the apparatus,via the extracorporeal blood circuit and access device and into thepatient.

This problem has been addressed, for example in WO2009/044220 A1 where ablood treatment apparatus includes a membrane device that comprises ablood chamber and a fluid chamber separated by a semipermeable membrane.A grounding device is connected to a treatment fluid discharge line bymeans of a tubular connector made of an electrically-conductive plasticmaterial. The grounding device can disconnect the grounding connectionif a leakage current measured on a patient connected to the apparatusexceeds a predetermined value.

Further prior art is reflected by US2009177149 A1 where various kinds ofleakage currents are addressed, and by U.S. Pat. No. 4,155,852 A whichrelates to a blood treatment apparatus that incorporates an electricallyisolated flux heater.

The techniques mentioned above are generally capable of reducing therisk of a patient being subject to an electrical shock. However, it isbelieved that the risk can be further reduced in case a blood treatmentapparatus experiences an electrical failure. This is particularlyrelevant when the blood treatment apparatus is intended for home use,where relatively higher safety requirements typically are required.

SUMMARY

It is an object of the invention to at least partly overcome one or morelimitations of the prior art. In particular, it is an object to providea blood treatment apparatus that may reduce the risk of a patient beingsubjected to electrical shock if an electrical failure occurs.

Hence a blood treatment apparatus is provided, which comprises: a bloodtreatment unit; a blood line configured to extract blood from a bloodsource, pass the blood through the blood treatment unit and delivertreated blood to a target vessel; a fluid line configured to extractelectrically conductive treatment fluid from a fluid source, pass thetreatment fluid through the blood treatment unit and deliver usedtreatment fluid to a fluid sink; and a flow divider arranged in thefluid line and configured to separate treatment fluid in the fluid lineinto to a first fluid section and a second fluid section, therebyelectrically isolating the fluid sections such that electrical currentflowing in the fluid line between the fluid sections is limited.

Limiting the electrical current may here include completely preventingan electrical current from flowing between the sections. By electricallyisolating the fluid sections a grounding connection to the fluid sink isbroken. Since this grounding connection is broken, a patient connectedto the apparatus is electrically floating in the sense that there is noconnection that may pass a current through the patient. Thereby is therisk of subjecting the patient to an electrical shock significantlyreduced.

In this context, it should be noted that the sink is generally the onlyitem that connects a typical blood treatment apparatus to the ground,and that common treatment fluids are electrically conductive. This isalso true for configurations were water is drawn from a water source andmixed with a concentrate to form the treatment fluid, since the water istypically de-ionized and thereby not electrically conductive.

Electrically isolating the fluid sections may be understood aspreventing a predetermined current from flowing between the fluidsections of the fluid that is conveyed within the fluid line. Thispredetermined current must not be zero but may not exceed a value thatis harmful for a patient. Thus, the flow divider is developed with theintention to electrically isolate the fluid sections. From this followsthat the flow divider is intentionally configured to prevent a patientconnected to the blood treatment apparatus from being subjected toelectrical shock. For this purpose the flow divider may be of a typethat has been verified for assuring that it provides electricalisolation. The electrical isolation may typically comprise isolationthat assures that a patient may not be subjected to a harmful electricalshock. It may also be said that the flow divider is of a type that hasbeen verified for its capability to reduce or prevent a current fromflowing between the fluid sections. In any case, the electricalisolation provided by the flow divider is both known and intentional. Ofcourse, the flow divider may incorporate more functionality than theelectrical isolation of fluid sections, such as the function oftransporting fluid in the fluid sections.

The electrical isolation provided by the flow divider may not be seen asan “accidental” or implicit electrical isolation that is achieved by acomponent arranged in the fluid line without the intentional purpose ofproviding the electrical isolation. This is true since“accidental”/implicit electrical isolation does not mean that a patientin fact is protected from an electrical shock.

As will be described below, the flow divider may be of several typeswhich have all verified for assuring that electrical isolation isprovided.

An advantage with the blood treatment apparatus lies in that a patientis proactively protected from electrical shock, in comparison with othersystems that have a more reactive character in the sense that protectionis initiated after a fault has occurred, i.e. when a patient already mayhave suffered some injury.

The fluid line may comprise an upstream fluid line and a downstreamfluid line, where the downstream fluid line is connected to a fluidoutlet of the blood treatment unit for delivering the used treatmentfluid to the fluid sink, and wherein the flow divider is arranged in thedownstream fluid line.

The flow divider may be configured to separate the treatment fluid inthe fluid line into multiple fluid sections, thereby breaking up a flowof treatment fluid in the fluid line.

The flow divider may be configured to provide a gas gap in the fluidline for generating the separation of the treatment fluid. Typically,the gas may be air that is drawn form the environment surrounding theblood treatment apparatus.

The flow divider may be configured to periodically open and close thefluid line for generating the separation of the treatment fluid. Thismay, for example, mean that the flow divider is configured toperiodically open and close the fluid line by periodically compressingand thereby occluding the fluid line.

The flow divider may comprise a drip chamber for generating theseparation of the treatment fluid.

The flow divider may comprise a first opening device and a secondopening device, the opening devices configured to periodically open andclose the fluid line for generating the separation of the treatmentfluid. The first and second flow dividers may be arranged in series orin parallel in the fluid line. When arranged in parallel the flowdividers are typically arranged in a respective branch line of the fluidline. Examples of opening devices include e.g. valves, pump and clamps,i.e. at least one of the opening devices may comprise a clamp, valveand/or pump.

The flow divider may comprise a peristaltic pump for generating theseparation of the treatment fluid. The peristaltic pump may comprise atleast two rollers configured to periodically compress the fluid line.The peristaltic pump may be referred to as a roller pump, and therollers may be referred to as a “shoes” or “wipers”. The peristalticpump electrically isolates the fluid sections such that electricalcurrent flowing in the fluid line between the fluid sections is limited.As previously indicated, the electrical isolation is deliberatelyprovided and is thus intentional. This means that the peristaltic pumpmay be of a peristaltic pump type that has been verified in respect ofits capability of providing electrical isolation. This is also true forthe general flow divider described above, i.e. the flow divider may beof a flow divider type that has been verified in respect of itscapability of providing electrical isolation.

The fluid line may comprise a buffer chamber configured to cooperatewith the flow divider, for generating the separation of the treatmentfluid in the fluid line.

The flow divider may be configured to electrically isolate the first andsecond fluid sections such that the electrical current is limited to apredetermined value. Specifically, the flow divider may be configured toelectrically isolate the first and second fluid sections such that theelectrical current is limited to maximum 500 μA, 50 μA or 10 μA.

The blood treatment apparatus may comprise a control unit configured tomeasure an electrical voltage over a section of the fluid linedownstream the flow divider. More specifically, the control unit may beconfigured to verify that the measured electrical voltage is below apredetermined value.

Also, the blood treatment apparatus may comprise a control unitconfigured to verify (i.e. measure) if an electrical current flowsbetween the first and second fluid sections. In principle, measuring avoltage and verifying a current are here functionally equivalent.

In further detail, the control unit may comprise a first connectorarranged in the fluid line upstream the flow divider and a secondconnector arranged in the fluid line downstream the flow divider, suchthat the control unit may apply a voltage over the connectors anddetermine a current thereby flowing in the treatment fluid between theconnectors. Applying a voltage and determining a current is hereequivalent to feeding a current between the first connector and thesecond connector and determining a resulting voltage there over.

As an addition or alternative to the connectors upstream and downstreamthe flow divider, the control unit may comprise two connectorsdownstream the flow divider and the control unit may then be configuredto measure a voltage over the two downstream connectors. Thismeasurement may be continuous or intermittent, and, if a measuredvoltage is above a predetermined value, the control unit may initiate asignal that indicates that the flow divider does not longer provide thedesired electrical isolation.

The control unit may be configured to monitor if the current exceeds apredetermined current value. This is equivalent to monitoring if avoltage is below a predetermined voltage value (for the above equivalentcase of feeding a current between the connectors and determining aresulting voltage there over).

The control unit may be configured to break a power supply to the bloodtreatment apparatus, if the current exceeds the predetermined currentvalue (or if the voltage is below a predetermined voltage in theequivalent case).

A previously indicated, the flow divider may be of a flow divider typethat has been verified in respect of its capability of providingelectrical isolation. Being verified may typically involve arranging theflow divider in a fluid line, applying a voltage over the flow dividerand measuring if an electrical current passes the flow divider as aresult of the applied voltage. Other, corresponding verification methodsmay be used just as well.

According to another aspect a method is provided for manufacturing theblood treatment apparatus described above, including all embodimentsthereof. The manufacturing comprises the step of arranging the flowdivider in the fluid line of the blood treatment apparatus, wherein themanufacturing of the blood treatment apparatus has been preceded by averification that the flow divider is of a type that separates treatmentfluid in the fluid line into to the first fluid section and the secondfluid section, such that the flow divider electrically isolates thefluid sections and thereby limits any electrical current flowing in thefluid line between the fluid sections.

The method of manufacturing includes steps for arranging all othercomponents comprised in the blood treatment apparatus. However, themanufacturing is always preceded by the verification of the flowdivider.

The verification preceding the manufacturing may include verifying thatthe flow divider electrically isolates the fluid sections such that theelectrical current is limited to maximum any of 500 μA, 50 μA and 10 μA.

According to another aspect a method is provided for verifying a flowdivider, the flow divider configured to be arranged in a fluid line of ablood treatment apparatus and to separate treatment fluid in the fluidline into a first fluid section and a second fluid section, therebyelectrically isolating the fluid sections such that electrical currentflowing in the fluid line between the fluid sections is limited. Themethod comprises the steps of: applying a voltage over a first connectorand a second connector, the first connector arranged in the fluid lineupstream the flow divider and the second connector arranged in the fluidline downstream the flow divider; and measuring a current resulting fromthe applied voltage. The verification method may comprise verifying thatthe electrical current is limited to maximum any of 500 μA, 50 μA and 10μA.

The described method of verification is equivalent to verifying if avoltage downstream the flow divider is below a predetermined level. Morespecifically, then the method may comprise the steps of: feeding acurrent through the flow divider; and measuring a voltage over a firstconnector and a second connector, where both connectors are arranged inthe fluid line and downstream the flow divider.

The various methods may include any of the features described above inassociation with the blood treatment apparatus and shares thecorresponding advantages. Still other objectives, features, aspects andadvantages of the invention will appear from the following detaileddescription, from the attached claims as well as from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example,with reference to the accompanying schematic drawings, in which

FIG. 1 illustrates a blood treatment apparatus according to a firstembodiment,

FIG. 2 a illustrates a test configuration for verifying that a flowdivider electrically isolates two fluid sections,

FIG. 2 b illustrates an alternative test configuration that isfunctionally equivalent with the test configuration of FIG. 2 a,

FIG. 3 illustrates a blood treatment apparatus according to a secondembodiment,

FIG. 4 illustrates a blood treatment apparatus according to a thirdembodiment,

FIG. 5 illustrates a blood treatment apparatus according to a fourthembodiment,

FIG. 6 illustrates a blood treatment apparatus according to a fifthembodiment,

FIG. 7 is a flow chart of a method for verifying that a flow dividerelectrically isolates two fluid sections, in combination with a methodfor manufacturing a blood treatment apparatus, and

FIG. 8 illustrates an embodiment of a blood treatment apparatusconfigured to detect a leakage current.

DETAILED DESCRIPTION

With reference to FIG. 1 a blood treatment apparatus 2 forextracorporeal blood treatment is illustrated. The blood treatmentapparatus 2 comprises a blood treatment unit 10 and a blood line 20 witha blood pump 23 arranged to draw blood from a blood source 21, pass theblood through the blood treatment unit 10 (which then may treat theblood) and deliver the treated blood to a target vessel 22. Theconfiguration of the blood line 20 and the blood treatment unit 10 isimplemented according to known techniques and may include various othercomponents and control units generally used in blood treatmentapparatuses. The blood source 21 and target vessel 22 may be a patientthat receives blood treatment but may also be bags of blood that arehandled by operators.

The blood treatment apparatus 2 has also a fluid line 30 arranged todraw treatment fluid (dialysate) from a fluid source 31, pass thetreatment fluid through the blood treatment unit 10 and deliver usedtreatment fluid to a fluid sink 32. The fluid sink 32 may, for example,be a drain or sewer.

Within the blood treatment unit 10 the treatment fluid interacts withthe blood in a manner known within the art, such that the treated bloodmay be delivered to the target vessel 22. The fluid line 30 is dividedinto an upstream fluid line 33 with a fluid pump 35 that deliverstreatment fluid to the blood treatment unit 10, and a downstream fluidline 34 connected to the fluid sink 32. Thus, the upstream fluid line 33is connected to a fluid inlet 11 of the blood treatment unit 10 whilethe downstream fluid line 34 is connected to a fluid outlet 12 of theblood treatment unit 10.

The downstream fluid line 34 comprises a flow divider 40 that isarranged to separate (used) treatment fluid in a first fluid section 51and a second fluid section 53. Even though the fluid sections 51, 53 areseparated they are still within the downstream fluid line 34 in thesense that the fluid composing the fluid sections 51, 53 are conveyedinside the fluid line 30. The flow divider 40 is in the illustratedembodiment a peristaltic pump 141 that periodically occludes thedownstream fluid line 34, which in this case may be made of a flexibleplastics material that may be compressed while it regains its originalshape after the compression is released. The upstream fluid line 33 maybe made of the same material, which has electrically isolatingproperties, such as materials like PVC, silicon rubber, thermoplasticelastomer etc. The occlusion separates the fluid in to the first fluidsection 51 and the second fluid section 53, where the point ofseparation is defined by the location where the peristaltic pump 141occludes the downstream fluid line 34.

The peristaltic pump 141 comprises a first roller 1411, a second roller1412 and a third roller 1413 that compress the downstream fluid line 34.The downstream fluid line 34 is arranged around the peristaltic pump 141such that at least one roller always fully compresses the downstreamfluid line 34. Thus, when one of the roller starts to release anoccluding pressure on the downstream fluid line 34, the next roller hasalready achieved full compression of the downstream fluid line 34. Itmay hence be assured that the fluid is always separated into (at least)a first fluid section 51 and a second fluid section 53.

The peristaltic pump 141 is not an ordinary peristaltic pump even thoughits principle layout may correspond to conventional peristaltic pumps.In detail, the peristaltic pump 141 is developed with the purpose ofassuring that an electric current flowing from the first fluid section51 to the second fluid section 53 is limited or prevented. Theperistaltic pump 141 is therefore of a type that has been verified inrespect of its capability of providing electrical isolation.

In detail, the flow divider 40 is configured to electrically isolate thefirst and second fluid sections such that the electrical current islimited to maximum 500 μA, 50 μA or 10 μA. These figures apply for allembodiments of a flow divider described herein as well as for otherconceivable flow dividers.

The peristaltic pump 141 as well as the more general flow divider 40 maybe controlled by a control device 70 for obtaining e.g. a properocclusion of the downstream fluid line 34. In this particular embodimentthe peristaltic pump 141 may be used as a mean for transporting thetreatment fluid through fluid line 30, and the control device 70 mayalso control the flow rate.

With further reference to FIG. 2 a an illustration is given of a testconfiguration for verifying that the flow divider 40, e.g. in the formof the peristaltic pump 141, electrically isolates the fluid sections51, 53. The test configuration is set up for a fluid line 34′ thatcorresponds to the downstream fluid line 34 of FIG. 1, by arranging theflow divider 40 in the fluid line 34′ between a first connector 63′ anda second connector 64′. A voltage U₁ is applied over the connectors 63′,64′ and the test configuration includes a resistor 69 with a resistanceR. The applied voltage U₁ may be an AC voltage or DC voltage, and may begalvanically isolated (floating). A current meter 67 measures a currentI flowing in the illustrated circuit, which then is the current flowingfrom the first connector 63′, through the flow divider 40 and to thesecond connector 64′. The measured current is zero (0) in case the flowdivider provides complete electrical isolation.

The configuration of FIG. 2 a can be verified for assuring that itoperates properly, for example by connecting a cable between theconnectors 63′, 64′ such that the current I may flow there between.

An alternative embodiment of the test configuration may also be used,which has four connectors to the fluid path; two for applying a currentand two for measuring voltage, in a so called 4-point measurement. Onecurrent connector and one voltage connecter is then placed on each sideof the flow divider.

With reference to FIG. 2 b another embodiment of a test configuration isshown, which is functionally equivalent with the configuration of FIG. 2a. This test configuration is set up for a fluid line 34′ by arrangingthe flow divider 40 upstream two connectors 63′, 64′ over which avoltage U₁ may be measured. A current unit 67′ is connected to a firstcurrent connector 63″ and to a second current connector 64″ arranged ona respective side of the flow divider 40, for feeding a current Ithrough the flow divider 40. If the measured voltage U₁ is zero, thenthe flow divider 40 provides complete electrical isolation.

By using the test configuration of FIG. 2 a the peristaltic pump 141 ofFIG. 1 that electrically isolates the fluid sections 51, 53 may beproperly configured or adjusted. In detail, the occluding force exertedby the rollers 1411-1413 on the fluid line 34 is adjusted such that thecurrent I is minimized. When performing tests and adjusting theperistaltic pump 141, it could be shown that the peristaltic pump 141may isolate the fluid sections 51, 53 to that extent that the current Inever exceeded 8 μA. Depending on the position of the rollers 1411-1413, it was observed that the measured current varied between 0-8 μA.Also, when the flow divider is a roller pump then the test configurationmay be employed for verifying if the roller pump occludes properly, e.g.at start up (so called priming) of the blood treatment apparatus.

As an alternative to using a peristaltic pump, any suitable type of pumpmay be used as long as it operates in a manner that always keep thesections 51, 53 separated such that electrical isolation is assured(i.e. verified). Examples of principal types of pumps that may be usedinclude positive displacement pumps (such as gear pumps, rotary vanepumps and roller pumps) and reciprocating-type pumps (such as pistonpumps, diaphragm pumps). Such pumps must of course be verified asdescribed above as well as (most likely) adjusted for increasing thelevel of separation. In other words, conventional pumps (i.e. unverifiedpumps) may not be used since they do not electrically isolate the fluidsections 51, 53 in the sense required herein.

Turning back to FIG. 1, as an alternative, the blood treatment apparatus2 may include a control unit 60 that may apply a voltage over a firstconnector 63 and a second connector 64. The first connector 63 isconnected to the downstream fluid line 34 at a position upstream theflow divider 40, while the second connector 64 is connected to thedownstream fluid line 34 at a position downstream the flow divider 40.The connectors 63, 64 are in electrical contact with the treatment fluidbut do not obstruct the flow of treatment fluid, and does not allow anytreatment fluid to escape from the fluid line 30. The control unit 60applies a voltage via a combined voltage source and current meter 61.The voltage source/current meter 61 operates in a manner similar to thecircuit shown in FIG. 2 a.

During operation of the blood treatment apparatus 2 the rollers1411-1413 of the peristaltic pump 141 ensure that the fluid line 30 isalways occluded at a varying position. When the fluid line 30 isoccluded, the walls of the fluid line 30 meet each other and therebyseparate the treatment fluid. Since the fluid line 30 is made of anelectrically isolating material no current or a maximum current of 8 μApasses between the separated fluid sections 51, 53. From this followsthat an electrical ground with the fluid sink 32 is in principle brokenwhich significantly decreases the risk of being subjected to electricalshock, for example if some component of the blood treatment apparatus 2malfunctions such that an electrical current may be transferred to apatient, for example via the blood treatment unit 10 and the blood line20.

Also, during the operation the control unit 60 applies via the voltagesource/current meter 61 a voltage over the first connector 63 and thesecond connector 64. The voltage source/current meter 61 provides areading of any current flowing between the connectors 63, 64 via theflow divider 40. The voltage is either continuously or at regular timeintervals applied over the connectors 63, 64 and if a current It isdetected a proper action may be taken. For example, if the current isabove 10 μA, 50 μA or 500 μA the control unit 60 may break a powersupply 68 to the blood treatment apparatus 2. The power supply 68 istypically a conventional current source that feeds the blood treatmentapparatus 2 with an electrical current. The control unit 60 providesadditional safety in that the flow divider 40 may be regularly verifiedin terms of its capability to electrically isolate the fluid sections51, 53. A suitable voltage value to apply generally depends on whatcurrent level shall be measured, on the type of flow divider 40 used aswell as on other components of the blood treatment unit. A suitableinterval for the verification may be each time the blood treatmentapparatus 2 is prepared for treatment of a new patient.

It should be observed that the control unit 60 does not replace theverification that the flow divider 40 is of a type that provideselectrical isolation. Instead, the verification performed by the controlunit 60 is an additional safety precaution that is performed for theflow divider 40 that is a part of the blood treatment apparatus 2.

It should also be understood that the voltage source/current meter 61 isequivalent to a unit that may send a current through the connectors 63,64 via the flow divider 40 and measure a resulting voltage, in whichcase the control unit 60 may e.g. break the power supply to the bloodtreatment apparatus 2 if the voltage is below a predetermined value.Here, applying a voltage and measure a resulting current is functionallythe same as feeding a current and measuring a resulting voltage.

With reference to FIG. 3 another embodiment of a flow divider 40 isillustrated. In this case the flow divider 40 comprises a drip-chamber143 that separates the treatment fluid into the first fluid section 51and second fluid section 53 by forming drops in the drip-chamber 143.The drip-chamber 143 may here comprise all shower-like structures,including configurations that are open to the surrounding environment(i.e. without a closed or sealed drip chamber).

A pump 35′ is arranged upstream the drip-chamber 143. Apart from thepump 35′ and the flow divider 40 being a drip-chamber 143, the othercomponents are the same as in the blood treatment apparatus 2 of FIG. 1.For this reason the complete blood treatment apparatus 2 is notillustrated in FIG. 3, but only the downstream fluid line 34.

The drip-chamber 143 is not an ordinary drip-chamber even though itsprinciple layout and principles of operation may correspond toconventional drip-chambers. In detail, the drip-chamber 143 is developedfor the purpose of assuring that an electric current flowing from thefirst fluid section 51 to the second fluid section 53 is limited. Thedrip-chamber 143 is therefore of a type that has been verified inrespect of its capability of providing electrical isolation. Thisincludes adjusting e.g. the drip-forming rate and drip height so thatany current flowing between the fluid sections 51, 53 is properlylimited.

With reference to FIG. 4 another embodiment of a flow divider 40 isillustrated. In this case the flow divider 40 comprises a first flowstopper 36 and a second flow stopper 37. The flow stoppers 36, 37 arearranged in series in the downstream fluid line 34, and a first bufferchamber 39 is arranged between the blood treatment unit 10 and firstflow stopper 36 while a second buffer chamber 38 is arranged between theflow stoppers 36, 37. The flow stoppers 36, 37 may be e.g. pumps, valvesor clamps that may be opened and closed by a control device 70′. Thedownstream fluid line 34 may include a pump 35′ arranged upstream theflow divider 40, for transporting the treatment fluid forwards towardsthe fluid sink 32.

In operation, the control device 70 intermittently opens and closes theflow stoppers 36, 37 such that the treatment fluid may flowintermittently from the blood treatment unit 10 to the fluid sink 32.However, before one flow stopper is opened the other is closed, andthereby the treatment fluid is always separated into the first fluidsection 51 and the second fluid section 53.

Apart from the flow divider 40 in form of the flow stoppers are otherparts of the blood treatment apparatus in this embodiment similar withthe blood treatment apparatus 2 illustrated in FIG. 1. The flow divider40 is in this embodiment developed with the purpose of assuring that anelectric current flowing from the first fluid section 51 to the secondfluid section 53 is limited. Thus, even though the flow stoppers 36, 37may have the principal form of a conventional pump, clamp or valve, theflow stoppers 36, 37 (pumps/clamps/valves) are not of commonly knowntypes since they are developed with the purpose of assuring that anelectric current flowing from the first fluid section 51 to the secondfluid section 53 is limited. The flow stoppers 36, 37(pumps/clamps/valves) are therefore of a type that has been verified inrespect of its capability of providing electrical isolation. Thisincludes adjusting e.g. the closing or occluding properties of the flowstoppers so that any current flowing between the fluid sections 51, 53is properly limited.

Tests have been performed by using clamps as flow stoppers that occludethe downstream fluid line 34 at sections made of the flexible materialdiscussed in connection with FIG. 1. Such tests show that the fluidsections 51, 53 may be separated to the extent that no electricalcurrent at all may flow between them. Similar results have been obtainedwhen properly adjusting the flow stopping properties of a 2-way 24 Vmagnet valve.

With reference to FIG. 5 another embodiment of a flow divider 40 isillustrated. In this case the flow divider 40 comprises a first 3-wayvalve 36′ and a second 3-way valve 37′. The downstream fluid line 34comprises a pump 35′ upstream the flow divider, a first buffer chamber38′ and a second buffer chamber 39′ arranged in parallel, as can be seenin the figure. Apart from this the blood treatment apparatus 2 issimilar with that of FIG. 1.

During operation the 3-way valves 36′, 37′ are controlled by the controldevice 70 in that the first 3-way valve 36′ feeds treatment fluid to thefirst buffer chamber 38′ when the second 3-way valve 37′ draws treatmentfluid form the second buffer chamber 39′. Thereafter the first 3-wayvalve 36′ feeds treatment fluid to the second buffer chamber 39′ whilethe second 3-way valve 37′ draws treatment fluid form the first bufferchamber 38′. Before changing to/from which buffer chamber treatmentfluid is fed/drawn, the 3-way valves are fully closed and thereby thefirst fluid section 51 and the second fluid section 53 are alwaysseparated. The separation provides electrical insulation between thefluid sections 51, 53, and the two 3-way valves 36′, 37′ are developedwith the purpose of limiting an electric current flowing from the firstfluid section 51 to the second fluid section 53. Thus even though the3-way valves 36′, 37′ may have a principal form of a conventional 3-wayvalve, they are not of a commonly known type since they are developedwith the purpose of assuring the limitation of an electrical current.

With reference to FIG. 6 another embodiment of a flow divider 40 isillustrated. In this case the flow divider 40 comprises an air injector142 that is controlled by the control device 70 to blow air or anothergas into the downstream fluid line 34. A pump 35′ is arranged upstreamthe flow divider 40, in the downstream fluid line 34. During operationair is blown/injected into the downstream fluid line 34 at regularintervals such that a number of air (gas) gaps 52, 54 are created. Theair gaps 52, 54 separate the treatment fluid into a number of sections51, 53, 55, for example into the first fluid section 51 and the secondfluid section 53.

The flow divider 40 in form of the air injector 142 is developed withthe purpose of limiting an electrical current flowing between the fluidsections 51, 53, and tests have shown that a current may be completelyprevented (i.e. full limitation is obtained) by the air-injection.Suitable sizes of the air gaps and suitable intervals of injection (sizeof and distance between the air gaps) may be empirically determined.

Other embodiments that provide an air gap are conceivable. For example,it is possible to arrange an air inlet in the downstream fluid line anda suction pump downstream the air inlet. The suction pump is thenoperated to provide a flow rate that is greater than a flow rate oftreatment fluid from the fluid source, such that air is drawn into thefluid line from the air inlet and mixed with the treatment fluid. Theair mixed with the treatment fluid separates the treatment fluid into anumber of sections, and sufficient electrical isolation can be obtainedby drawing in e.g. twice as much air from the air inlet as treatmentfluid from the fluid source.

With reference to FIG. 7 a method of manufacturing any of theembodiments of the blood treatment apparatus described above isillustrated. The method comprises the step 205 of manufacturing theblood treatment apparatus 2 which is done according to known techniques,but includes the step 205′ of arranging in the blood treatment apparatusany of the flow dividers described above. However, the step 205 ofmanufacturing the blood treatment apparatus is always preceded by a step201 of verifying that the flow divider is of a type that electricallyisolates the fluid sections.

The step of verification 201 includes verifying that the flow dividerelectrically isolates the fluid sections such that the electricalcurrent is limited to maximum any of 500 μA, 50 μA and 10 μA. Theverification may be done by using the test equipment of FIG. 2 a.

Since the verification is an important step when manufacturing the bloodtreatment apparatus, it may be said that the verification is a part ofthe manufacturing process even though it must not be performed beforeevery step of manufacturing a blood treatment apparatus. It sufficesthat the step 201 of verification is performed once for the type of flowdivider that is used. After the step 201 of verification the step 205 ofmanufacturing a blood treatment apparatus may be performed numeroustimes.

With reference to FIG. 8 the downstream fluid line 34 of an alternativeblood treatment apparatus is illustrated. Reference numerals similarwith reference numerals in other figures represent similar items. Theblood treatment apparatus 2 includes a grounding device 71 that isconnected to the downstream fluid line 34 and which may disconnect thegrounding connection if a leakage current measured on a patientconnected to the blood treatment apparatus exceeds a predeterminedvalue.

If the leakage current exceeds the predetermined value then the controldevice 70′ activates a flow divider 40 (e.g. in form of a pump, valve orclamp) such that the treatment fluid in the fluid line is separated intoto the fluid sections 51, 53. Patent document WO 2009/044220 exemplifieshow leakage current may be measured, and is incorporated by reference.

The control unit 60 and the control device 70 described herein typicallyincludes a respective one or more processing units that may executesoftware instructions, i.e. computer program code that carry out theabove described operations. For this purpose the blood treatmentapparatus may include a computer-readable memory that stores thesoftware instructions. These may for development convenience be writtenin a high-level programming language such as Java, C, and/or C++ butalso in other programming languages, such as, but not limited to,interpreted languages. Also, the control unit 60 and the control device70 may be embodied as a single unit.

Moreover, the flow divider and any parts that support its function,including the connectors, may just as well be arranged in the upstreamfluid line. However, it is generally more advantageous to have the flowdivider in the downstream fluid line, since it is then closer to thesink. For increasing the level of electrical insulation it is possibleto arrange several flow dividers in the fluid line. The flow dividersmay then be of the same type or of different types. Several flowdividers in combination may be seen as one flow divider.

Although various embodiments of the invention have been described andshown, the invention is not restricted thereto, but may also be embodiedin other ways within the scope of the subject-matter defined in thefollowing claims.

1. A blood treatment apparatus comprising: a blood treatment unit, ablood line configured to extract blood from a blood source, pass theblood through the blood treatment unit and deliver treated blood to atarget vessel, a fluid line configured to extract an electricallyconductive treatment fluid from a fluid source, pass the treatment fluidthrough the blood treatment unit and deliver used treatment fluid to afluid sink, and a flow divider arranged in the fluid line and configuredto separate the treatment fluid in the fluid line into to a first fluidsection and a second fluid section, thereby electrically isolating thefluid sections such that electrical current flowing in the fluid linebetween the fluid sections is limited.
 2. The blood treatment apparatusaccording to claim 1, wherein: the fluid line comprises an upstreamfluid line and a downstream fluid line, the downstream fluid line isconnected to a fluid outlet of the blood treatment unit for deliveringthe used treatment fluid to the fluid sink, and the flow divider isarranged in the downstream fluid line.
 3. The blood treatment apparatusaccording to claim 1, wherein the flow divider is configured to separatethe treatment fluid in the fluid line into multiple fluid sections,thereby breaking up a flow of treatment fluid in the fluid line.
 4. Theblood treatment apparatus according to claim 1, wherein the flow divideris configured to provide a gas gap in the fluid line, for generating theseparation of the treatment fluid in the fluid line.
 5. The bloodtreatment apparatus according to claim 1, wherein the flow divider isconfigured to periodically open and close the fluid line, for generatingthe separation of the treatment fluid in the fluid line.
 6. The bloodtreatment apparatus according to claim 1, wherein the flow dividercomprises a drip chamber, for generating the separation of the treatmentfluid in the fluid line.
 7. The blood treatment apparatus according toclaim 1, wherein the flow divider comprises a first opening device and asecond opening device, the opening devices configured to periodicallyopen and close the fluid line for generating the separation of thetreatment fluid in the fluid line.
 8. The blood treatment apparatusaccording to claim 7, wherein at least one of the opening devicescomprises a clamp.
 9. The blood treatment apparatus according to claim7, wherein at least one of the opening devices comprises a valve. 10.The blood treatment apparatus according to claim 1, wherein the flowdivider comprises a peristaltic pump.
 11. The blood treatment apparatusaccording to claim 10, wherein the peristaltic pump comprises at leasttwo rollers configured to periodically compress the fluid line.
 12. Theblood treatment apparatus according to claim 1, wherein the fluid linecomprises a buffer chamber configured to cooperate with the flowdivider, for generating the separation of the treatment fluid in thefluid line.
 13. The blood treatment apparatus according to claim 1,wherein the flow divider is configured to electrically isolate the firstand second fluid sections such that the electrical current is limited toa predetermined value.
 14. The blood treatment apparatus according toclaim 1, wherein the flow divider is configured to electrically isolatethe first and second fluid sections such that the electrical current islimited to maximum of 0.0005 amps.
 15. The blood treatment apparatusaccording to claim 1, wherein the flow divider is configured toelectrically isolate the first and second fluid sections such that theelectrical current is limited to maximum of 0.0005 amps.
 16. The bloodtreatment apparatus according to claim 1, wherein the flow divider isconfigured to electrically isolate the first and second fluid sectionssuch that the electrical current is limited to maximum of 0.00001 amps.17. The blood treatment apparatus according to claim 1, comprising acontrol unit configured to measure an electrical voltage over a sectionof the fluid line downstream the flow divider.
 18. The blood treatmentapparatus according to claim 1, comprising a control unit configured toverify if an electrical current flows between the first and second fluidsections.
 19. The blood treatment apparatus according to claim 18,wherein the control unit comprises a first connector arranged in thefluid line upstream the flow divider and a second connector arranged inthe fluid line downstream the flow divider, such that the control unitmay apply a voltage over the connectors and determine a current therebyflowing in the treatment fluid between the connectors.
 20. The bloodtreatment apparatus according to claim 19, wherein the control unit isconfigured to monitor if the current exceeds a predetermined currentvalue.
 21. The blood treatment apparatus according to claim 20, whereinthe control unit is configured to break a power supply to the bloodtreatment apparatus, if the current exceeds the predetermined currentvalue.
 22. The blood treatment apparatus according to claim 1, whereinthe flow divider provides electrical isolation.
 23. A method ofmanufacturing a blood treatment apparatus comprising: a flow divider ina fluid line of the blood treatment apparatus, wherein the manufacturingof the blood treatment apparatus has been preceded by a verificationthat the flow divider is of a type that separates treatment fluid in thefluid line into to the first fluid section and the second fluid section,such that the flow divider electrically isolates the fluid sections andthereby limits electrical current flowing in the fluid line (30) betweenthe fluid sections.
 24. A method of verifying a flow divider configuredto be arranged in a fluid line of a blood treatment apparatus and toseparate treatment fluid in the fluid line into to a first fluid sectionand a second fluid section, thereby electrically isolating the fluidsections such that electrical current flowing in the fluid line betweenthe fluid sections is limited, the method comprising the steps of:applying a voltage over a first connector and a second connector, thefirst connector arranged in the fluid line upstream the flow divider andthe second connector arranged in the fluid line downstream the flowdivider, and measuring a current resulting from the applied voltage.